Apparatus for the development of latent electrostatic images



Oct. 15, 1968 K. JONS ET AL 3,405,683

APPARATUS FOR THE; DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Filed June 19, 1964 2 Sheets-Sheet l INII/IENTORS Xurz Jams Ger/7am Afarx Z M ATTO 5y Oct. 15, 1968 K. JONS ET AL 3,405,683

APPARATUS FOR THE DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Filed June 19, 1964 I 2 Sheets-Sheet 2 Ger/7am Marx Z. M ATTOR r United States Patent 3,405,683 APPARATUS FOR THE DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Kurt Jons, Wiesbaden-Biebrich, and Gerhard Marx,

Mainz-Kastel, Germany, assignors, by mesne assignments, to Azoplate Corporation, Murray Hill,

Filed June 19, 1964, Ser. No. 376,392 Claims priority, application Germany, June 22, 1963,

4 Claims. of. 118-637) ABSTRACT OF THE DISCLOSURE The liquid developers used in electrophotography comprise a dispersion of solid toner particles in a liquid having dielectric properties. During development, the toner particles, which bear a charge, are attracted to the electrophotographic material in accordance with the charge image upon it, whereas the dielectric liquid fiow's off. The result is a visible image.

The normal practice is to bring the electrophotographic material into contact with the liquid developer by dipping, by drawing it through a container which contains the liquid developer, or by bringing it into contact with a thin film of liquid developer on the surface of a roll.

These procedures have the disadvantage that it is not normally possible to bring sufiicient toner particles into effective contact with the electrophotographic material in the time available, and it is therefore difiicult to achieve the desired dense and homogeneous coloring of the image areas. Furthermore, the toner particles have a tendency to deposit on the non-image areas, with the result that corrective measures, such as the application of a biasing potential, must often be employed.

When the developing apparatus includes a rotating roll which carries the film of liquid developer on its surface, the rotation of the roll produces a residual image, constituted by a deposit of toner particles conforming with the image previously developed on the newly supplied electrophotographic material.

The invention provides a process for the development of latent electrostatic images, which comprises feeding the electrophotographic material to be developed through the nip of a pair of rolls and spraying liquid developer on the surface of the material bearing the latent image as it approaches the nip and also on that portion of the surface, approaching the nip, of that roll which contacts the latent image.

The invention includes an apparatus for performing this process which includes a pair of nip rolls for engaging and feeding forward the electrophotographic material and at least one nozzle for spraying liquid developer both on the surface of the electrophotographic material carrying the latent image as it approaches the nip and also on the portion, approaching the nip, of the roll which contacts the latent image.

The process and apparatus according to the invention avoid the disadvantages mentioned above because a suflicient quantity of toner particles is brought into contact with every point of the latent image on the electrophotographic material to ensure uniform covering with toner particles of the image areas. Moreover, the non-image areas remain practically free of toner particles, since such particles are washed from these areas by the sprayed streams of developer liquid. Furthermore, the sprayed stream of developer liquid directed on the surface of the roll removes therefrom toner particles adhering to it as the result of the preceding developing operation and the residual image is thus destroyed.

The invention will now be further described with reference to the accompanying schematic drawings in which:

FIGURE 1 shows diagrammatically the basic principle of the invention, and

FIGURES 2-4 are cross-sectional views of alternative forms of developing apparatus according to the invention.

The apparatus shown in FIGURE 1 includes a feed table B, formed with a gap. The electrophotographic material A, which has a latent charge image a on its upper side is fed along the table B towards the nip between a pair of rolls C C which rotate in the direction indicated by the arrows. Before reaching and while passing through the nip the material A is sprayed with liquid developer supplied through a nozzle D. A stream d of spray contacts the material A before it reaches the nip and another stream d of spray impinges upon the surface of the roll C removing from ittoner particles which adhere to the surface in an image-wise fashion as a result of the preceding developing operation.

FIGURE 2 shows a preferred embodiment of the present invention. The electrophotographic material, placed on a feed table 2 with the latent electrostatic image facing downwardly, is fed by a pair of feed rolls 3 and 4 against the surface of a guide 5, which guides the electrophotogr-aphic material towards the nip formed by a pair of rolls 6 and 7. The roll 6 is driven by a motor, and the roll 7 is rotated by the friction of the material passing through the nip and is either mounted resiliently or spaced a small distance from the roll 6. The material 1 is fed through the nip to a feed table 8. While traveling from the nip of rolls 3 and 4 to the nip of rolls 6 and 7, the surface of the material bearing the latent image is sprayed with liquid developer, ejected from a nozzle 15, to which developer 14 contained in a tank 20 is supplied by a pump 16 through a tube 11.

The nozzle 15, which extends over the entire width of the material 1, also sprays developer on the surface of the roll 6. Since the liquid developer is sprayed under pressure, both the image-carrying side of the material 1 and the surface of the roll 6 receive a large amount of developer. This ensures a copious supply of toner particles to the electrophotographic layer in the limited time available, effective removal from the surface of the roll 6 of the aforementioned residual image, and washing away of toner particles from the non-image areas of the material 1. Excess developer, which collects in the space between the roll 6 and the guide 5 flows through a slot 18 into a tray 19 and thence to the tank 20, from which it is recirculated by the pump 16.

The developed electrophotographic material is discharged from the feed table 8 by squeeze rolls 9 and 10, which may be urged resiliently towards one another and which remove excess liquid from the surface of the material 1. The roll 9, which comes into contact with the reverse side of the material, preferably has a rubber surface coating, e.g. of rubber having a Shore hardness of 30-40" or of sponge rubber. The roll 9 is cleaned by the liquid which runs off into the tray 19. The surface of the roll 10 should be as smooth as possible and is provided with a wiper which may consist of a Teflon scraper 12 and an absorbent material 13. The roll 10 may, however, also be cleaned by means of a stream of liquid pumped from the tank 20.

The guide is made of metal or plastic material and has a machined, smooth surface. Its shape is of no particular importance, since its sole purpose is to guide the material 1, without undue bending or curvature, from the rolls 3 and 4 to the rolls 6 and 7.

The roll 6 may be made of metal. Its surface may be smooth, or it may be milled or grooved. The roll 6 may have a layer of plastic material, such as a thermosetting or thermoplastic resin. The nozzle may have a single outlet, or two or more outlets. By providing multiple outlets it is possible to arrange for the jet of liquid to impinge upon the material at a wider angle than that illustrated or to provide for the material to be sprayed from several directions over a greater length. The same applies to the spraying of the surface of the roll 6.

In the construction of FIGURE 3, the rolls 6 and 7 and the guide 5 of FIGURE 2 are replaced by a plurality of rolls 6a, 7a, 7b, 7c, and 7d which results in a prolonged contact between the electrophotographic material passing through the roll hips and the film of developer liquid on the surface of the rolls. The electrophotographic material is fed to the rolls in the direction indicated by the arrow 1a. It is immaterial whether the side of the material carrying the latent image faces upwardly or downwardly. To permit this and to ensure effective spraying of the rolls and the electrophotographic material, a plurality of spraying nozzles 15a to 15e are provided. The feed rolls, squeeze rolls, liquid storage tank, the pump, and the remaining elements of the apparatus are as shown in FIGURE 2.

In the construction shown in FIGURE 4, the roll 6 of FIGURE 2 is replaced by a number of smaller rolls 21a to 21d. Opposite each of these smaller rolls is a second larger roll 7e to 7h, so that the electrophotographic material to be developed passes in succession through four roll nips. Here again, an intensified spraying of the image to be developed is ensured by the provision of a plurality of spraying nozzles 15 to 15 It is again immaterial which side of the electrophotographic material faces upwardly.

All rolls and guides which come into contact with the electrophotographic material to be developed are insulated, in the sense that they are neither in electrically conductive contact with one another nor grounded. It is, of course, also possible to provide an electric biasing field but this gives no additional advantages.

The various forms of apparatus described yield excellent high-contrast images which are available for use almost immediately after the material has been discharged from the apparatus. The images are completely free of background.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. An apparatus for developing a latent electrostatic image on an electrophotographic material comprising means to feed the electrophotographic material, a pair of rotatable nip rolls through which the electrophotographic material is fed, nozzle means mounted adjacent the nip adapted to simultaneously spray a liquid developer containing an electroscopic material onto said latent electrostatic image before and during passage of said electrophotographic material into the nip and onto the nip roll which contacts the sprayed latent image.

2. An apparatus according to claim 1 in which a plurality of nip rolls are arranged in series.

3. An apparatus according to claim 1 in which a plurality of nip rolls and a plurality of nozzles are arranged in series.

4. An apparatus according to claim 1 in which the feed means comprises a pair of feed rolls.

References Cited UNITED STATES PATENTS 2,140,289 12/ 1938 Hurtt et al. 118-206 X 2,653,566 9/1953 Worden 118-63 2,785,083 3/1957 Robinson 117-111 2,877,133 3/1959 Mayer 118-637 3,139,808 7/1964 Ritzerfeld et a1. 117-37 X 3,155,546 11/1964 Dirks 118-637 3,187,716 6/ 1965 Peterson et al 118-70 X 3,241,521 3/1966 Labombarde 117-111 3,242,902 3/ 1966 Ulary 118-637 3,249,088 5/1966 Ostensen 118-637 3,301,699 1/1967 Mozzi 118-259 X FOREIGN PATENTS 938,349 10/ 1963 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

E. I. CABIC, Assistant Examiner. 

